The sampling frame for the Study is New York State (NYS), exclusive of New York City. The Study, which began September 4, 2007, is designed to use a population-based sampling strategy to recruit and compare the development of a matched-exposure cohort of infants, i.e., infants identified from pregnancies conceived with the help of infertility treatment, as noted in the NYS Perinatal Data System, and infants who were conceived without such therapies. The infertility treatment exposure is the basis for the sampling because of its relative rarity. For the primary cohort, infants identified as having been conceived by infertility treatment (exposed) are to be enrolled as participants at 3-5 months of age (gestation-corrected, if necessary) and followed longitudinally until age 36 months (3 years), along with a cohort unexposed infants, frequency-matched for residence within a NYS Regional Perinatal Network and plurality of birth. All co-twins of Study participants are to be enrolled simultaneously and either their outcomes noted (e.g., stillbirth, neonatal mortality), or they are to be followed (secondary cohort) on the same schedule as Study participants, although the co-twins will not be considered as part of the primary cohort. All higher order multiples (triplets, quadruplets) are also to be enrolled and followed on the same schedule, regardless of exposure status. The period of recruitment for the referent (primary) birth cohort began in September, 2008, and is on-going. Parents of infants born in NYS will be asked to participate in the Study for three years by: (a.) completing an initial questionnaire about the pregnancy, including, for example, confirmation of infertility treatment, time-to-pregnancy, infant feeding, and other demographic and socioeconomic factors (i.e., maternal education, occupation) and confounders associated with motor and social development;(b.) completing a standardized screening instrument that addresses their childs motor and social development at chronologic or gestation-corrected ages 4, 8, 12, 16, 20, 24, 30, and 36 months;and (c.) providing information on the child's growth and medical history (e.g., illnesses, diagnoses of birth defects, major impairments). Information on growth and medical history will be assembled in journal format from physicians examination data. Records will be linked to other pertinent health records (e.g., early intervention programs, WIC, birth defect or cancer registries). Several additional components have been added in this year: (a.) a detailed ART history by linking with the Society for Assisted Reproductive Technology (SART) cycle-based database;(b.) the acquisition of residual blood specimens left over from mandatory neonatal screening and laboratory testing for biomarkers and environmental exposures. The blood specimens are archived at the Wadsworth Center Laboratories (New York State Department of Health), and (c.) plans for the administration of a standardized assessment for diagnosing developmental disabilities using a battery of empirically validated and reliable instruments at 24-30 months of age for all infants and children who fail any of the neurodevelopmental screens.